The participation of these two polluting superpowers is essential to building a global consensus heading into next year's United Nations conference on climate change.

BEIJING AND WASHINGTON — U.S. Energy Secretary Steven Chu and Commerce Secretary Gary Locke are in Beijing this week to talk about climate change with Chinese leaders. The hope is to open the nation's market to American clean technology products while nudging China toward committing to hard targets for reducing greenhouse gas emissions.

They have their work cut out for them.

Although China is rapidly expanding its use of alternative energy to curb dependence on fossil fuels, it's favoring its own wind and solar manufacturers over foreign suppliers. And despite recently surpassing the United States as the world's largest emitter of carbon dioxide, China has stated repeatedly that the U.S. and other industrial powers must take the lead on cutting emissions.

The issue is pitting industrial countries against the developing world over what role each should play in slowing potentially devastating global warming. At the Group of 8 summit meeting in Italy last week, China and other emerging powers declined to commit to specific goals for slashing heat-trapping gases by 2050. They said their rise from poverty shouldn't be derailed by the rich nations responsible for most of the damage.

The participation of the U.S. and China is essential to building a global consensus heading into next year's United Nations conference on climate change. Any accord that doesn't include these two polluting superpowers would largely be considered a failure. But carbon caps are proving a point of friction between the trading partners.

"The United States and China have developed a very strong, advantageous relationship because of the economy, and by and large, it's been mutually beneficial," said Dan Dudek, chief economist for the Environmental Defense Fund. "But when it comes to climate change and energy, that simple equation starts to break down. What they're looking for now is a path to similar interests."

Obama administration officials, and the president himself, are peddling cautious optimism in Washington about Chinese efforts on global warming. In an interview with energy reporters late last month, Obama sounded a cooperative tone about working with China and India to reduce emissions.

"We're going to be able to take a look at what they're doing," he said, "and to the extent that they are taking steps within their own economies to make progress, I think we're going to be able to help leverage even greater gains internationally."

The mood is decidedly more combative on Capitol Hill, particularly among Republicans, many of whom insist that China must act aggressively on emissions before the U.S. will.

China's response to climate change has been "complex and contradictory," Sen. Richard G. Lugar (R-Ind.), one of the few GOP senators that Democrats believe could eventually support a climate bill, said at a committee hearing last month.

He added: "The American domestic debate on the issue will be profoundly influenced by perceptions of China's willingness to set aside doctrinaire positions and agree to verifiable steps to limit greenhouse gas emissions."

China is in the throes of massive urbanization that will add 350 million residents to its cities in the next 20 years -- a migration of rural dwellers that will require dramatic increases in energy capacity. Those new urbanites will want access to air conditioning, cars and electronics that developed nations have long enjoyed.

"Why can't these people have the same rights as Americans?" said Hu Tao, program coordinator of the United Nations China Climate Change Partnership Framework. "With a cap [on emissions], that means in the future we won't have the right to use these things. That's not realistic."

Recognizing the growing environmental crisis, Beijing has launched its own set of domestic policies to reduce pollution while resisting international accords on emissions that they believe will interfere with determining their own destiny.

Beijing has committed $462 billion to scaling up renewable energy by 2020. China has increased wind power by 100% each of the last three years. And although still modest in scope, China plans to boost solar power capacity tenfold in the next decade. Meanwhile, smaller and more inefficient coal plants are being phased out.

China's wind farms can be seen in the far-flung West on the outskirts of desert cities such as Urumqi. Towering turbines are also being installed offshore near Shanghai. And China boasts millions of inexpensive, solar-powered household water heaters. The nation is the world's top producer of solar photovoltaic panels, although 95% of them are exported.

But China remains highly dependent on dirty coal, building coal-fired power plants at a breakneck pace. Some of China's chief polluters ignore laws to use clean technology because it's cheaper to pay a fine.